afaik there isn't, whta you could do however is to first get all terrain code used in the curent map with wesnoth.get_terrain and wesnoth.get_map_size. end then get information about those ces with wesnoth.get_terrain_info

Scenario with Robots SP scenario (1.11/1.12), allows you to build your units with components, PYR No preperation turn 1.12 mp-mod that allows you to select your units immideately after the game begins.

If you don't need to include terrains from campaigns and/or add-ons but only need core terrains, then you could include the core terrain.cfg into some container, using [set_variables], which would then give you all the core terrain definitions as a simple WML array.